For the light source of projection display apparatus, high-power light sources that produce a large amount of heat such as metal halide lamps, super-high pressure mercury lamps, etc., have been used in order to ensure a bright projected image. These light sources that produce a large amount of heat may thermally deform the surrounding structural parts due to elevation in temperature, or may reduce the lifetime of the arc tubes. In particular, there is a close correlation between the life of the arc tube and temperature, so that cooling for keeping the optimal temperature range is required.
Light generated by the light source is shaped into an image through an optical engine, then is enlarged by a projection lens to be projected on a screen. The optical engine is provided with a plurality of optical parts such as liquid crystal panels etc.; these optical parts are also elevated in temperature due to transmission and reflection of strong light. This elevation in temperature makes the operation of the liquid crystal panels unstable and changes the properties of various kinds of optical parts, deteriorating the projected image and shortening the lives of the optical parts. That is, suppressing elevation in temperature of the optical parts will maintain the optical performance and lengthen the life of the optical parts, so that cooling of the optical parts is essential to enhance the performance and reliability of the apparatus.
Under these circumstances, presentations that use a projection display apparatus have become widespread with the spread of personal computers, and the chances of using a projection display apparatus at high altitude locations such as mountainous regions are increasing.
However, when a projection display apparatus is used in a high altitude area, there is a greater increase in the temperature of the optical parts, including the lamp and liquid crystal panels, than in the case when the projection display apparatus used at a low altitude. This occurs because the air is thin at highlands due to low atmospheric pressure, hence heat transfer of the heat generated in the apparatus to the air is suppressed.
As the related art to solve this problem, there is disclosed the following technology in which a pressure sensor is provided for a projection display apparatus to detect atmospheric pressure, and the rotation rate of the air-cooling fan is increased in accordance with the detected atmospheric pressure.
Disclosed in Japanese Patent Application Laid-open 2004-157365 is a projector including a cooling mechanism and a cooling control selecting means for selecting and setting up the drive control of this cooling mechanism in accordance with the altitude of the place it is to be used where so as to be able to a secure sufficient cooling effect even if it is used at highlands.
Japanese Patent Application Laid-open 2000-194072 discloses a projection display apparatus, which includes: a fan for cooling the housing interior; a temperature detecting element for detecting the temperature in the vicinity of the liquid crystal light bulb; and a control unit for correcting the temperature detected by the temperature detecting element based on a predetermined temperature correcting value, controlling the rotation rate of the fan based on the corrected temperature and performing on/off control of the power source to the lamp, so as not to lower reliability depending on a change in the environment where the apparatus is used.
Japanese Patent Application Laid-open 2002-258237 discloses a liquid crystal projector, which includes: a temperature sensor for detecting the interior temperature; an air pressure sensor for detecting the outside air pressure; and a control unit for controlling the rotation rate of a cooling fan based on the detected temperature and outside air pressure, and automatically performs suitable control of the cooling fan in accordance with the air pressure at the area where it is used.
Japanese Patent Application Laid-open 2006-91611 discloses a projection video display apparatus including a system control circuit receiving the input of the air pressure data output from an air pressure sensor and the airflow data output from an airflow sensor, in which the system control circuit stores a control table for regulating the additional voltage value to the fan power supply, which is set based on the air pressure value and airflow value, so as to be able to perform optimal cooling control as much as possible even if filter-clogging has occurred.
However, these related technologies are aimed at maintaining the temperature of the lamp portion and various optical parts by increasing the rotation rate of the air-cooling fan to enhance the cooling effect, and there have been two serious problems.
The first problem is that use of the apparatus at highlands entails a significant temperature rise of the heat generating part, hence it is necessary to greatly increase the rotation rate of the air cooling fan, thereby giving rise to a problem of increased noise. For example, when a projection display apparatus is used at an altitude of 1,500 m, a temperature rise of 5 to 15° C. occurs in the optical parts of the optical engine, and the temperature of the arc tube of the lamp produces a temperature rise of 30° C. to 50° C. When this temperature rise is handled by increasing the rotation rate of the fan, the rotation rate of the fan has to be increased to about 1.8 times, and this will increase noise by about 10 dB. The noise level is acoustically felt to be twice as laud because of this value, therefore this is problem.
The second problem is that because there is an upper limit to the rotation rate of the air-cooling fan, an altitude of around 2,300 m is the limit for keeping optical parts of an apparatus at a desired temperature even if this leads to an increase in noise. For example, about 1500 meter is the limit for a typical projection display apparatus in the related art, and even for an apparatus that has “highland mode” for increasing the rotation rate of the fan, the limit is around 2,300 m.